Improve Send Error Sheet UX

[ovitrif]

I fixed the toast message in this PR but the error sheet message is also misleading, I will remove in next PR, then on this error screen we'll have parity with iOS:

That screen needs work on both platforms. Design has some improvements to status quo but needs to be adjusted somewhat. For LN payments "Transaction" is not accurate, should be "Payment". And we should try to show a user actionable error description as well as we can.

Originally posted by @pwltr in #825 (comment)